The Impact of a Stealth CME on the Martian Topside Ionosphere
Smitha V. Thampi, C. Krishnaprasad, Govind G. Nampoothiri, Tarun K. Pant
MMNRAS , 000–000 (2020) Preprint 19 February 2021 Compiled using MNRAS L A TEX style file v3.0
The Impact of a Stealth CME on the Martian Topside Ionosphere
Smitha V. Thampi (cid:63) , C. Krishnaprasad, Govind G. Nampoothiri, and Tarun K. Pant
Space Physics Laboratory, Vikram Sarabhai Space Centre, Thiruvananthapuram 695022, India
19 February 2021
ABSTRACT
Solar cycle 24 is one of the weakest solar cycles recorded, but surprisingly the declining phase of it had a slow CME whichevolved without any low coronal signature and is classified as a stealth CME which was responsible for an intense geomagneticstorm at Earth (Dst = -176 nT). The impact of this space weather event on the terrestrial ionosphere has been reported. However,the propagation of this CME beyond 1 au and the impact of this CME on other planetary environments have not been studiedso far. In this paper, we analyse the data from Sun-Earth L1 point as well as from the Martian orbit (near 1.5 au) to understandthe characteristics of the stealth CME as observed beyond 1 au. The observations near Earth are using data from the SolarDynamics Observatory (SDO) and the Advanced Composition Explorer (ACE) satellite located at L1 point whereas those nearMars are from the instruments for plasma and magnetic field measurements on board Mars Atmosphere and Volatile EvolutioN(MAVEN) mission. The observations show that the stealth CME has reached 1.5 au after 7 days of its initial observations at theSun and caused depletion in the nightside topside ionosphere of Mars, as observed during the inbound phase measurements ofthe Langmuir Probe and Waves (LPW) instrument on board MAVEN. These observations have implications on the ion escaperates from the Martian upper atmosphere.
Key words:
Sun: coronal mass ejections (CMEs), Sun: helio-sphere, planets and satellites: terrestrial planets, planets and satel-lites: atmospheres, planet–star interactions, Earth
Coronal Mass Ejections (CMEs) are eruptions on the Sun, by whichsolar plasma and magnetic field are expelled into the heliosphere.CME eruption processes involve an energy storage phase, whichmay be the product of flux emergence or photospheric flows fol-lowed by an energy release phase. There are different physical mech-anisms proposed for the eruption of CMEs, which include tethercutting or flux cancellation mechanism (Moore et al. 2001; Amariet al. 2003), shear motion (Aly 1990), kink instability (Török &Kliem 2004), torus instability (Kliem & Török 2006) and magneticRayleigh–Taylor instability (Mishra et al. 2018). There are differ-ent models to explain the solar eruptions like flux emergence model(Feynman & Martin 1995), Catastrophe model (Forbes & Isenberg1991), magnetic breakout model (Antiochos et al. 1999), reconnec-tion model (Wyper et al. 2017) and forced reconnection (Srivastavaet al. 2019). Based on the morphological evolution, the CMEs areclassified as halo CMEs, partial halo CMEs, narrow CMEs, andCMEs with low coronal signatures. The CMEs from the Sun, whichhave virtually no identifiable surface or low corona signatures areoften referred to as stealth CMEs (Robbrecht et al. 2009). These aretypically slow CMEs with a speed less than 500 km s − . Studies haveshown that they can originate either from the quiet Sun region (Maet al. 2010) or from an active region (O’Kane et al. 2019). They canalso be originated near the open field lines or coronal holes or fromfaint flux rope eruptions (Adams et al. 2014; Lynch et al. 2016; Nitta& Mulligan 2017). Pevtsov et al. (2012) observed that a plasma chan-nel without a clear filament structure could also become the source region of stealth CMEs. A recent study on the magnetic field configu-ration in which the stealth CME occur, show distinct episodes of flareribbon formation in the stealth CME source active region (O’Kaneet al. 2020). In stealth CMEs, the energy storage and release sequencedo happen, but the energy release is weak, which is probably asso-ciated with the magnetic reconnection during the eruption or due toan instability process (O’Kane et al. 2019). The stealth CMEs haveno usual solar eruption warning signs in the lower corona, making itdifficult for space weather predictions and therefore these may leadto unpredictable geomagnetic activity and ionospheric storms. Maet al. (2010) have done a statistical analysis of the source location ofthe CMEs during solar minima and reported that almost one third ofthe CMEs occurring during the solar minimum period are of stealthtype. Zhang et al. (2007) have studied the connection between thesolar eruptions and intense magnetic storms on Earth (Dst<-100 nT)during Solar Cycle (SC) 23. They found that 12% of the total CMEswere launched without low coronal signatures. When we consider thegeoeffectiveness of CMEs, several studies have shown that the geo-effectiveness is higher for slow CMEs (Ma et al. 2010; Lynch et al.2016; Nitta & Mulligan 2017). Since the stealth CMEs are typicallyof slow velocities, understanding their geoeffectiveness is consideredto be very important. Typically being slow, they spend a long timein the interplanetary space and near–space environments of planets,and have high interaction time with other solar wind structures andplanetary magnetospheres, some of these interactions probably helpto enhance their geoeffectiveness (Liu et al. 2016). For instance, Tsu-rutani et al. (2004) found that some slow ICMEs surprisingly causedintense geomagnetic storms. However, it is still unclear how slowCMEs lead to enhanced geoeffectiveness by interacting with othersolar wind structures. Similarly, the impacts of such stealth CMEson environments of planets like Mars are not reported. Since theobservations and models both show an enhancement in escape rateson unmagnetized planets like Mars and Venus during space weather © a r X i v : . [ a s t r o - ph . E P ] F e b Smitha Thampi et al. events like CMEs (Jakosky et al. 2015; Brain et al. 2016), understand-ing the statistics of the stealth CMEs and their impacts are importantfor quantifying the planetary atmospheric escape processes.The declining phase of the SC–24 had a stealth CME (Mishra& Srivastava 2019), which caused an intense geomagnetic stormat Earth (Dst = -176 nT), which is the third most intense storm ofthe SC–24 (Abunin et al. 2020; Piersanti et al. 2020). Astafyevaet al. (2020) mentioned it as a ‘surprise geomagnetic storm’ andstudied its impact on Earth’s thermosphere and ionosphere usingboth space–based (the Swarm constellation, GUVI/TIMED) andground–based (GPS receivers, magnetometers, SuperDARN) instru-ments. However, the arrival and impact of this event on other plan-etary bodies have not been reported yet. In this study, we report thesolar wind and magnetic field observations from a vantage point nearMars to understand the arrival of this slow stealth CME and showthe response of Martian topside ionosphere to this event.
The solar observations are taken from Solar Dynamics Observatory(SDO)/Atmospheric Imaging Assembly (AIA; Lemen et al. (2012))( https://sdo.gsfc.nasa.gov/ ) and the Solar and HeliosphericObservatory (SOHO) Large Angle and Spectrometric Coronagraph(LASCO)-C2 ( https://cdaw.gsfc.nasa.gov/CME_list/ ). Wehave also used the Wang-Sheeley-Arge (WSA)–ENLIL+Cone model(Odstrcil 2003; Mays et al. 2015) from ENLIL Solar Wind Predic-tion ( http://helioweather.net/ ) for understanding the relativeplanetary positions and the global heliospheric context. The Inter-planetary Magnetic Field (IMF) and solar wind speed near 1 au, aswell as the Sym-H (representing the ring current) variations at Earthare obtained from the NASA Space Physics Data Facility (SPDF)OMNIWeb data center ( https://omniweb.gsfc.nasa.gov/ ).The datasets from the Mars Atmosphere and Volatile Evolu-tioN (MAVEN) instruments are from the Planetary Data System( https://pds.nasa.gov/ ). The solar wind speed and IMF valuesnear Mars are obtained from the Solar Wind Ion Analyzer (SWIA;Halekas et al. (2015)) and Magnetometer (MAG; Connerney et al.(2015)) instruments aboard MAVEN spacecraft. SWIA is an energyand angular ion spectrometer that measures the energy and angulardistributions of solar wind ions of energy between 25 eV and 25keV with 48 logarithmically spaced energy steps. MAG is a fluxgatemagnetometer that measures the intensity and direction of the IMF.The method to determine the upstream solar wind and IMF condi-tions from MAVEN is described by Halekas et al. (2017), and isused in several studies (e.g. Lee et al. (2017); Krishnaprasad et al.(2020)). The Langmuir Probe and Waves (LPW; Andersson et al.(2015)) instrument on board MAVEN is used for the in situ electrondensity and electron temperature measurements [Level 2, version 3,revision 01 (V03_R01)]. The Neutral Gas and Ion Mass Spectrom-eter (NGIMS; Mahaffy et al. (2014)) observations of MAVEN areused to understand the variations of O +2 and O + ion densities inthe Martian ionosphere. NGIMS is a quadrupole mass spectrometerwhich measures the composition of neutrals and thermal ions, in themass range 2-150 amu with unit mass resolution. The NGIMS Level2 ion data version 08, revision 01 (V08_R01) are used. Figures 1(a), 1(c), and 1(e) show the images of the solar disk as seenin the 211 Å images from the AIA on board SDO on 20 August2018. These images show the signatures of a filament structure andtwo coronal holes which produces fast solar wind. The quiescentfilament structure passed over the coronal hole and partially eruptedto a Coronal Plasma Channel (CPC). Figure 1(b), 1(d) and 1(f)show the region of the coronal plasma channel, at different stagesof development. Several other instances of the development of thisplasma channel leading to the filament eruption are given in Mishra& Srivastava (2019). It is suggested that the spreading coronal plasmachannel might have interacted with an open field line of the coronalhole (Mishra & Srivastava 2019), leading to a jet–like eruption. Thehot coronal plasma channel is visible in other EUV filters of AIAas well (Mishra & Srivastava 2019). Following this, a flux rope hasalso evolved and erupted above the coronal plasma channel. So,there are three ejections with very faint evidence in the lower corona,which merged with each other to form a complex stealth CME, whichtraveled through the interplanetary space which was observed in theSTEREO-A HI-2 (Heliospheric Imager-2) field of view on 24 August2018, 08:09 UTC (Mishra & Srivastava 2019). The lower part of theCME interacted with the terrestrial magnetosphere on 25 August2018. The features of the eruptions, their interplanetary propagationand the arrival at Earth are described in detail by Mishra & Srivastava(2019); Abunin et al. (2020); Chen et al. (2019); Piersanti et al.(2020). The HI images (Figure 11, Mishra & Srivastava (2019))further show that the CME arrived near the Mars on 27 August 2018.Figure 2 shows the WSA-ENLIL+Cone simulation snapshots dur-ing the passage of the stealth CME at Earth as well as during its arrivalat Mars. The color shows the solar wind radial velocity. During theCME arrivals at Earth and Mars, the velocity is low. However, there isa high speed stream possibly originated from the coronal hole. Chenet al. (2019) reported that after the filament eruption, the coronalhole merged with a dimming region on 21 August 2018. This couldbe the source of the fast solar wind stream, which followed the ICMEand arrived at the planets.Figure 3 shows the variation of IMF, solar wind velocity, protondensity as well as dynamic pressure observed near Mars by MAVEN.The total B as well as the components are shown in Figure 3a. Forcomparison, the Bz values observed at L1 are also shown in the figure.Along with the other solar wind parameters observed by MAVENshown in Figures 3(b-d), the near Earth values are also shown forcomparison. Apart from this, the Sym-H observed at Earth is alsoshown to depict the occurrence of the intense geomagnetic stormat Earth. It can be seen that, at Earth on 25-26 August the IMF Bzshows the signature of a magnetic cloud arriving at Earth. The IMFenhancement at Mars starts on 27 August and continues even on 28August. The peak southward component at Earth is ∼
16 nT, and thetotal B is as high as 19 nT (Mishra & Srivastava 2019). At Mars,the peak B field strength is ∼
10 nT. When the CME arrived, solarwind velocity near Earth was ∼
350 km s − which indicated thatthis was a slowly propagating CME. The solar wind velocity nearEarth further showed an increase because of the high speed stream,and the peak velocity was observed on 28 August. Near Mars, thesolar wind velocity was ∼
400 km s − , on the arrival of the ICME.The arrival of the high speed stream followed, with peak velocityobserved on 28 August. On both these planets, by the time the streamarrived, the magnetic field enhancements and fluctuations (due toCME) diminished, indicating that the CME already passed. Both at1 au and 1.5 au, the CME structure was therefore bracketed between MNRAS , 000–000 (2020) tealth CME at Mars the ambient slow wind and the high speed stream, thus enhancing theeffectiveness of interaction. Since MAVEN is in an elliptical orbit,it observes the upstream solar wind conditions only intermittently(Halekas et al. 2017), making it difficult to infer the exact eventarrival time at Mars. During August 2018, the inbound legs of the MAVEN spacecraftwere observing the nightside region from the near–dusk region tonear–midnight sector, and the outbound legs were observing the postmidnight sector. We make use of MAVEN in-situ observations fromthe inbound phase to understand the response to the ICME. The datafrom the outbound phase are not used because of the low signallevels (characteristic of deep nightside data, due to low plasma con-centrations). Observations during 24-26 August represent the typicalquiet time variation, and the observations on 27 and 28 August 2018represent the ‘event orbits’.Table-1 shows the details of the MAVEN orbits used in this study,such as variation in altitude, solar zenith angle (SZA), local solartime (LST), latitude, and longitude during inbound legs. These ob-servations pertain to the northern hemisphere of Mars where theinfluences of the crustal magnetic field are a minimum (Acuña et al.1999). It has been observed that during nightime, the largest peak iondensities are found near vertical crustal fields, which form cusps thatallow energetic electron precipitation, whereas smaller peak densi-ties are found near horizontal crustal fields, which hinder energeticelectron precipitation into the atmosphere (Girazian et al. 2017).However, these effects are observed over the southern hemisphere,where there are strong crustal fields. The variability of electron den-sity for the present event are mostly free from these effects, sincethe observations shown here are for the inbound leg, which covernorthern hemisphere.Figure 4a shows several LPW orbits during the event, compared tothe quiet time orbits. The quiet time orbit data are shown along withthe mean and standard deviation (error bars). The third, fourth, fifthand sixth orbits on 27 August 2018, and the first orbit on 28 August2018 show significant difference from the quiet time behavior. Above200 km, the topside electron densities are completely depleted dur-ing these orbits. There are a few data points in the electron densityprofile around 300-350 km altitude region in the profile correspond-ing to orbit 6 on 27 August 2018. However, these are points withvery low density values. It is reported that the signal-to-noise ratiosare reduced below electron densities of ∼
200 cm − (Fowler et al.2015). Therefore, we do not infer any information from these isolatedstructures. At 150-200 km, we only show that the topside electrondensities are completely depleted, compared to ‘quiet orbits’ duringthe space weather event. These gradients are similar to the ionopause-like density gradient reported earlier (Vogt et al. 2015). Figure 4bshows the NGIMS observations of O +2 and O + ion concentrationsfor the same period. It must be noted that NGIMS alternates betweenion and neutral modes, whereas LPW measures the electron densityin all orbits, and hence the signature is seen only in fewer orbits inNGIMS data. Similarly, the number of ‘quiet’ time profiles are alsofewer for the NGIMS observations, and hence the mean and the stan-dard deviations are not given. However, the feature that the topsideion densities are highly depleted during the ICME period is unmis-takably seen in the NGIMS observations as well. Figure 4c shows theelectron temperature observations from the LPW measurement dur-ing the event period, along with the quiet time profiles. The topsideelectron temperatures are enhanced during all the orbits where elec-tron density showed depletion. However, it may be noted that reduced signal-to-noise ratios at regions where electron densities are belowdensities of ∼
200 cm − also result in LP temperature measurementerrors increasing to 100% or more (Fowler et al. 2015), and thereforewe cannot infer these as the accurate profiles of T e during these days.Despite this, it is evident that the profiles during the ‘event orbits’show trends which are significantly different (with enhanced values)compared to ‘quiet orbits’. The CME event observed near the Sun on 20 August 2018 was a CMEwithout a preceding shock, and is classified as a stealth CME (Mishra& Srivastava 2019). The observations show that while reaching Mars,the maximum IMF was ∼
10 nT, which may be considered as anintense space weather condition at Mars. The solar wind velocityobserved near Mars was ∼
400 km s − , and this was a slow CMEinside a compression region between slow and fast solar winds, evenwhen it reached Mars.The slow, stealth CME impacted Martian topside ionosphere, andthe nightside plasma measurements show that the topside thermalionosphere is significantly depleted. The electron temperature mea-surements showed enhancements during this event period. Similarobservations were reported by Cravens et al. (1982) for the Venu-sian nightside ionosphere. On days when disappearing ionosphereswere observed by the OETP (Orbiter Electron Temperature Probe)aboard Pioneer Venus mission, the solar wind dynamic pressure wereconsiderably larger than average. It was shown that depleted and vari-able plasma densities throughout all or a major part of the nightsideVenusian ionosphere occurred during periods of large, coherent andhorizontal magnetic field events and associated with large solar winddynamic pressures. It was suggested that because dayside ionopauseis at low altitudes when the solar wind dynamic pressure is largeand the IMF is strong, the nightside ionosphere supplied by the day-to-night transport of plasma disappears. If the dayside ionosphere isseverely reduced then it is expected that the supply of ions to thenightside will be curtailed, and the large horizontal magnetic fieldwill inhibit the downward diffusion. As a result of these, the nightside ionosphere will be disappeared. The present observations showthat the same is true for Martian ionosphere also. It may also be notedthat since this was a slow CME with bulk solar wind velocity nearMars ∼
400 km s − , the outward flow could be weaker comparedto the CMEs with larger velocities. Even though the peak dynamicpressure was only ∼ The declining phase of solar cycle 24 had a slow stealth CME whichwas responsible for an intense geomagnetic storm at Earth withDst min of -176 nT. The propagation of this CME beyond 1 au andthe impact of this CME on Martian plasma environments are studied.The observations show that the stealth CME has reached 1.5 au after7 days of its initial observations at the Sun, with a peak magneticfield of ∼
10 nT . This CME caused depletion in the nightside topsideionosphere of Mars. The topside ionosphere also had higher electron
MNRAS , 000–000 (2020)
Smitha Thampi et al. temperatures compared to the ‘quiet’ values. Even with a peak dy-namic pressure as low as 5 nPa, the CME had efficiently impacted theMartian ionosphere, because the CME was slow, and was bracketedbetween the fast and slow solar winds. This is an unique example toshow how slow CMEs can affect the Martian ionosphere. As almostone third of the CMEs occurring during the solar minimum periodare of slow, stealth type (Ma et al. 2010), characterizing their impacton Martian ionosphere is important for constraining the ion escaperates.
ACKNOWLEDGEMENTS
The work is supported by the Indian Space Research Organisation(ISRO). We thank the staff of the ACE Science Center for pro-viding the ACE data and OMNIWeb team for providing the IMFand solar wind data. We gratefully acknowledge the MAVEN teamfor the data. We also acknowledge using solar observations fromSDO/AIA. The WSA-ENLIL+Cone model simulations are used fromENLIL Solar Wind Prediction. C. Krishnaprasad acknowledges thefinancial assistance provided by ISRO through a research fellow-ship. This research has made use of SunPy v2.0, an open-sourceand free community-developed solar data analysis Python package( https://sunpy.org/ ). DATA AVAILABILITY
The solar wind velocity and IMF at L1 point are obtained fromthe SPDF OMNIWeb data center ( https://omniweb.gsfc.nasa.gov/ ).The MAVEN data used in this work are taken from the NASAPlanetary Data System ( https://pds.nasa.gov/ ). The solar ob-servations are available at SDO/AIA ( https://sdo.gsfc.nasa.gov/ ). The WSA-ENLIL+Cone model simulations are used fromENLIL Solar Wind Prediction ( https://helioweather.net/ ). REFERENCES
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R., 2017, Nature, 544, 452Zhang J., et al., 2007, Journal of Geophysical Research: Space Physics, 112MNRAS000 , 000–000 (2020) t e a lt h C M E a t M a rs -1000" -500" 0" 500" 1000"1000"500"0"-500"-1000" Helioprojective Longitude (Solar-X) [arcsec] H e li o p r o j e c t i v e L a t i t u d e ( S o l a r - Y ) [ a r c s e c ] (a)AIA 211 A 2018-08-20 08:09:57 -100" 0" 100" 200" 300" 400"400"300"200" 30°15°0° 15°30°Helioprojective Longitude (Solar-X) [arcsec] H e li o p r o j e c t i v e L a t i t u d e ( S o l a r - Y ) [ a r c s e c ] Solar Longitude S o l a r L a t i t u d e (b) -1000" -500" 0" 500" 1000"1000"500"0"-500"-1000" Helioprojective Longitude (Solar-X) [arcsec] H e li o p r o j e c t i v e L a t i t u d e ( S o l a r - Y ) [ a r c s e c ] (c)AIA 211 A 2018-08-20 13:59:57 -100" 0" 100" 200" 300" 400"400"300"200" 30°15°0° 15°30°Helioprojective Longitude (Solar-X) [arcsec] H e li o p r o j e c t i v e L a t i t u d e ( S o l a r - Y ) [ a r c s e c ] Solar Longitude S o l a r L a t i t u d e (d) -1000" -500" 0" 500" 1000"1000"500"0"-500"-1000" Helioprojective Longitude (Solar-X) [arcsec] H e li o p r o j e c t i v e L a t i t u d e ( S o l a r - Y ) [ a r c s e c ] (e)AIA 211 A 2018-08-20 23:53:57 -100" 0" 100" 200" 300" 400"400"300"200" 30°15°0° 15°30°Helioprojective Longitude (Solar-X) [arcsec] H e li o p r o j e c t i v e L a t i t u d e ( S o l a r - Y ) [ a r c s e c ] Solar Longitude S o l a r L a t i t u d e (f) Figure 1.
The SDO/AIA 211 Å full disc images (a, c, d) and the zoomed view (b, c, d) during different stages of the filament eruption that occurred on 20 August 2018. M N R A S , ( ) Smitha Thampi et al.
Figure 2.
The WSA-ENLIL+Cone model inner heliospheric simulation snapshots showing the solar wind radial velocity (color contour) and IMF during stealthCME event of August 2018. The relative positions of Earth and Mars are also shown.Day/ UTC UTC Alt Alt Lon Lon Lat Lat SZA SZA LST LSTOrbit (hr) (hr) (km) (km) (deg) (deg) (deg) (deg) (deg) (deg) (hr) (hr)INBOUND From To From To From To From To From To From To27/Orbit 1 0.25 0.45 499.10 149.45 19.68 316.06 74.85 41.15 116.61 160.37 19.58 0.0227/Orbit 2 4.67 4.87 496.45 150.69 84.17 20.91 74.82 41.31 116.66 160.24 19.59 23.9927/Orbit 3 9.10 9.29 497.58 150.37 149.94 85.68 74.87 41.31 116.36 160.26 19.50 23.9827/Orbit 4 13.52 13.71 498.14 150.14 215.40 150.50 74.92 41.51 116.13 160.09 19.44 23.9627/Orbit 5 17.94 18.13 497.02 150.64 280.43 215.33 74.89 41.55 116.04 160.07 19.41 23.9427/Orbit 6 22.36 22.55 497.73 149.97 346.11 280.18 74.95 41.79 115.75 159.85 19.33 23.9128/Orbit 1 2.78 2.97 496.78 150.48 51.06 344.97 74.94 41.83 115.67 159.82 19.30 23.9028/Orbit 2 7.20 7.39 499.24 151.24 116.86 49.87 74.97 42.12 115.36 159.53 19.22 23.8728/Orbit 3 11.62 11.82 498.03 150.43 182.27 114.69 75.00 42.26 115.15 159.40 19.16 23.8524/Orbit 1 1.51 1.71 498.63 148.72 54.51 358.80 74.24 38.79 119.58 161.72 20.44 0.3524/Orbit 3 10.35 10.55 499.85 148.37 185.58 128.40 74.39 38.97 119.07 161.71 20.31 0.3124/Orbit 4 14.78 14.97 499.64 149.36 250.48 193.31 74.37 39.25 119.02 161.53 20.28 0.2824/Orbit 5 19.20 19.39 496.73 148.92 315.40 258.08 74.40 39.26 118.94 161.60 20.26 0.2725/Orbit 1 4.04 4.24 497.45 149.76 85.92 27.73 74.47 39.54 118.61 161.47 20.16 0.2325/Orbit 2 8.46 8.66 498.66 149.28 151.70 92.61 74.54 39.82 118.30 161.27 20.07 0.2025/Orbit 3 12.88 13.08 496.55 149.33 216.44 157.34 74.56 39.80 118.26 161.34 20.06 0.1925/Orbit 4 17.30 17.50 498.70 149.54 282.32 222.28 74.60 40.10 117.94 161.11 19.97 0.1625/Orbit 5 21.73 21.92 498.35 148.81 347.69 287.08 74.67 40.26 117.73 161.01 19.91 0.1426/Orbit 2 6.57 6.76 496.86 150.10 117.76 56.79 74.68 40.64 117.53 160.73 19.84 0.1026/Orbit 4 15.41 15.60 496.48 150.32 248.17 186.42 74.73 40.87 117.22 160.59 19.75 0.0626/Orbit 5 19.83 20.03 497.04 149.98 313.89 251.19 74.79 40.86 116.93 160.63 19.67 0.04
Table 1.
Periapsis pass time in UTC (with day of August 2018 and orbit of the day), altitudes, longitudes, latitudes, SZA, and LST for disturbed orbits (27/28August) and representative quiet orbits (24, 25, and 26 August) during the inbound legs of MAVEN [measurement below 500 km altitude].MNRAS000
Periapsis pass time in UTC (with day of August 2018 and orbit of the day), altitudes, longitudes, latitudes, SZA, and LST for disturbed orbits (27/28August) and representative quiet orbits (24, 25, and 26 August) during the inbound legs of MAVEN [measurement below 500 km altitude].MNRAS000 , 000–000 (2020) tealth CME at Mars
23 24 25 26 27 28 29 3010010 B ( n T ) (a) B Bx By Bz Bz (Earth)
23 24 25 26 27 28 29 30400500600 S W s p ee d ( k m / s ) (b) near Mars near Earth
23 24 25 26 27 28 29 300102030 S W D e n s i t y ( c m ) (c) near Mars near Earth
23 24 25 26 27 28 29 30Day of August 20180.02.55.07.510.0 S W D y n . P r e ss u r e ( n P a ) (d) near Mars near Earth S y m H ( n T ) Sym-H (Earth)
Figure 3.
IMF (a), solar wind speed (b), solar wind density (c) and dynamic pressure (d) observations during 23-31 August 2018, near Earth and Mars. TheSym-H variation, indicating the occurrence of an intense geomagnetic storm at Earth is also shown in (d). MNRAS , 000–000 (2020)
Smitha Thampi et al. Electron Density (cm )150200250300350400450500 A l t i t u d e ( k m ) (a) MAVEN-LPW Ion Density (cm )150200250300350400450500 A l t i t u d e ( k m ) (b) MAVEN-NGIMS
Quiet (O +2 )Quiet (O + )27/ orb. 2 (O +2 )27/ orb. 2 (O + )27/ orb. 4 (O +2 )27/ orb. 4 (O + )28/ orb. 1 (O +2 )28/ orb. 1 (O + )10 Electron Temperature (K)150200250300350400450500 A l t i t u d e ( k m ) (c) MAVEN-LPW
Figure 4. (a) The LPW observations during 27-28 August 2018, along with the typical quiet time variation. The 7 quiet orbits on 24, 25 and 26 August 2018,are shown as blue dots. The mean of the quiet time profiles is shown (black line) along with standard deviation. (b) The NGIMS O + (amu 16), and O +2 (amu32) observations during 27-28 August 2018, along with the typical quiet time variation. The quiet time variations are from observations on 26 August 2018. (c)The LPW Electron temperature estimates during 27-28 August 2018, along with the quiet time variation. Both LPW and NGIMS observations are during thethe inbound phase of the MAVEN spacecraft.MNRAS000